In recent years, bearing assemblies such as those disclosed in U.S. Pat. Nos. 3,726,574; 3,746,407; 3,891,282 and 3,918,773 have self-contained fluid pools. Those patents are assigned to the same assignee as the present invention. Such fluidic, low friction self-contained bearings are made possible by the development of magnetically responsive magnetizable fluid given the name ferrofluid by its developer, Dr. Ronald E. Rosensweig. Ferrofluid is described in Rosensweig's "Progress in Ferrohydrodynamics," Industrial Research, October, 1970, Vol. 12, No. 10, 36-40. Ferrofluid as defined therein is a dispersion of colloidal magnetic particles in a liquid carrier. These particles tend to align themselves with applied magnetic fields. It should be noted from the description of ferrofluid that ferrofluid need no necessarily contain iron or ferrous-type metal. It is only necessary, for a fluid to be so-called, that the fluid be magnetizable or capable of being influenced by magnetic fields. The term "magnetic fluid" is used interchangeably herein with the term "ferrofluid".
The bearings described in the above-identified letters patent each concentrate the magnetic field at particular axial positions along the shaft to produce a seal for the ferrofluid. Typically vanes, or the like, are used to distribute ferrofluid on the bearing surface to maintain a sufficient fluid thickness to support or lubricate the bearing.
More recently the assignee has filed U.S. patent application Ser. No. 34,549 on Apr. 30, 1979 for a "Seal for a Fluid Bearing", by Rena Fersht, et al., now U.S. Pat. No. 4,254,961. The bearing shown and described in that patent application also concentrates the magnetic field at the seal points, but the structure may be modified according to this invention.